Some kinds of window glasses are provided on at least one of their main surfaces (hereinafter occasionally referred to as a “print surface”) with a conductive ceramic fired body as a conductor in order to form antenna wires for receiving a variety of radio waves used in the applications such as digital broadcasting, televisions, radios, GPS and keyless entry systems, defoggers (hot wires), circuit wirings, etc. The window glasses of such a type are attached to vehicles, in particular, automobiles, and used therein as a front window, a rear window or a side window.
The conductive ceramic fired body is generally produced on a surface of the window glass by screen-printing a given pattern of a conductive ceramic paste containing silver and a glass component on the print surface of the window glass and subjecting the thus printed pattern of the conductive ceramic paste to heat treatment for calcining the paste. The thus produced conductive ceramic fired body exhibits a white color when viewed from a front side of the window glass having the print surface and a brown color when viewed from a rear side of the window glass opposite to the print surface. For this reason, in the case of window glasses having a deep color such as black which may be frequently used for vehicles, the portion of the window glass where the conductive ceramic fired body is formed tends to offend the eyes when viewed from an interior side of the vehicle, and tends to adversely affect an exterior design of the vehicle to a considerable extent when viewed from an exterior side of the vehicle, resulting in poor appearance thereof on both of the interior and exterior sides of the vehicle.
Incidentally, when the conductive ceramic fired body serving especially as antenna wires is formed in a vehicle, from the viewpoint of reducing its adverse influence on a vehicle body as one of conductive parts of the vehicle to ensure a good performance thereof, it is preferred that the conductive ceramic fired body be installed at a position as distant as possible apart from a flange portion (of the vehicle body) to which the window glass is mounted. In consequence, the conductive ceramic fired body must be installed in a visible region of the window glass which is remarkably noticeable by passengers, thereby causing such a tendency toward a poor appearance of an interior side of the vehicle.
To solve the above problems, Patent Document 1 discloses the invention concerning a window glass for vehicles in which the psychometric lightness L* value of a color of the antenna wires constituted of a fired body of a conductive paste when viewed from each of an interior side and an exterior side of the vehicle is limited to a predetermined value by adding a pigment or a color-developing agent to the conductive paste. Patent Document 2 discloses the invention concerning a film antenna formed by successively laminating a black-colored opaque adhesive, a resin film formed of polyethylene terephthalate, etc., an antenna element and a black-colored portion on a surface of a glass plate. In addition, Patent Document 3 discloses the invention concerning a conductive fired body having a surface layer in which a large amount of silver chloride is incorporated by subjecting the fired body to chemical treatment.
Patent Document 1: JP-A 2001-206056
Patent Document 2: JP 4021911
Patent Document 3: JP-A 2007-284276